A family study of biologic factors in schizophrenia has been initiated. Diagnostic evaluations on 12 families with more than one schizophrenic sibling, and the following biological studies, have been done: Computed Tomography (CT) was performed on ill and well sibling. Ventricular size was found to have a familial component and also to be significantly larger in the schizophrenic siblings compared with their well siblings and controls. HLA and other protein markers (immunoglobulin polymorphisms) were determined and linkage analysis performed. There was no linkage to the HLA or Gm loci in these families. Serum immunoglobulin levels (IgG, IgA, IgM) were found to have a familial component, but lower levels did not segregate with illness in families. Abnormal leukocyte counts, atypical lymphocytes, antinuclear antibodies, and antithymic antibodies were not present at an increased frequency in schizophrenics versus their family members and controls. Herpes simplex, cytomegalovirus and Epstein-Barr viral antibodies were determined in serum of all evaluated subjects. No differences in herpes simplex or cytomegalovirus antibody titres were found among patients and controls. Schizophrenics had significantly higher antibody titres against the Epstein-Barr early antigen than hospital staff members or other controls. No chromosomal abnormalities, including fragile X chromosome, were found in any of our patients.